Wheel Mythology?

Being a bit of a sceptic & scientifically trained I am continually amazed at the almost supernatural powers attributed to bike wheels.  

I know this one will cause a bit of a stink for some but here goes.  

The weight of your rim only has a very small effect on how you perform on a bike.

 

Check out this site:

 

http://biketechreview.com/reviews/wheels/63-wheel-performance

 

To summarise:

"So, what do all these numbers mean? It means that when evaluating wheel performance, wheel aerodynamics are the most important, distantly followed by wheel mass. Wheel inertia effects in all cases are so small that they are arguably insignificant."

 

There are other references out there citing the same thing.  

So, beware the marketing hype and even worse the reviews both online and in bike mags, does the phrase "these wheels spin up really fast" sound familiar.

 

Personally I think most of what people attribute to increased performance (read speed) is actually more to do with differences in wheel stiffness, aesthetics, sound (e.g. zipps) & cost.

 

Remember I am not talking about aerodynamics & total weight (bike + rider) here...more to come on that.

 

Cheers Chris

Tags: wheels

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Replies to This Discussion

Permalink Reply by Chris Adams on September 16, 2011 at 11:23

I read somewhere once where they said close your eyes & get someone to turn your bike upside down and then you spin the wheel with your little finger.  Get the person to change the wheel over for a wheel of different rim weight (say 250 g), spin again, & see if you can feel the difference.

I think it would be fairly difficult & it may be that the bearings cloud the decision.

 

btw, I haven't tried this.

 

cheers chris

Permalink Reply by Baron Von Thierry on September 15, 2011 at 22:08

analyticcycling - wheel calculations

Permalink Reply by Baron Von Thierry on September 15, 2011 at 22:34

http://www.analyticcycling.com/WheelsCritCorner_Page.html

 

Jumping From Criterium Corner

Our standard rider is on 32 spoke standard wheels. Our test rider is riding Specialized tri-spokes. Both riders jumped from a criterium corner with the same initial speed. The riders are the same in all other respects. For the same power output, which one will be ahead at the end of 100 meters? By how much?

The motion equations say that the rider on the Specialized wheels will be ahead by 18 cm after 100 meters, or about 0.015 seconds even though the Specialized wheels are heavier by 49 gm and have higher rotational inertia

Permalink Reply by Gemma K on September 15, 2011 at 22:41

They're very old numbers and data though.

Compare a 32h 'typical' wheelset now against some more modern offerings.  There's likely to be 500g+ difference, and with less rotational inertia, and improved aerodynamics (those specialized tri-spokes were heavy!).  the difference will be metre+, and that's just after one corner.... think how many laps/corners you do in a 1 hr hot dog crit...

Permalink Reply by Chris Adams on September 16, 2011 at 10:33

I guess the prob is, everyone is racing with sim wheels/bikes so any advantage is cancelled out.  

Permalink Reply by Chris Adams on September 16, 2011 at 11:07

Just did some calculations on Analyticcycling.com

 

Using the "Jumping From Criterium Corner" example above:

1. If I reduce the weight of the trispoke front wheel by 0.2 kg & rear by 0.3 kg (keeping aero & moment of inertia constant) the trispoke will now be ahead 0.02 s (0.24 m) after 100 m.

 

2. As well as the 0.2 + 0.3 kg weight reductions I reduced the moment of inertia of each trispoke by 25%, the trispoke will now be ahead 0.02 s (0.29 m).

 

cheers chris

Permalink Reply by Roger ... on September 23, 2011 at 16:14

all this science is very interesting but the one thing that makes really good wheels that you lot aren't talking about is spoke tension. (craftsmanship)

spoke tension isn't really able to be measured easily from wheel set to wheel set but it makes easily as much difference as pumping up your tyres to your performance. A couple of really well hand tensioned wheels give a remarkable difference to exactly the same wheels with the spokes not as tight. The heavier the rider the more important the spoke tension is.

So what I am saying is that choosing finest hubs rims and spokes isn't a guarantee of the quality of the end product. Just as buying a few balls of fine wool doesn't make an excellent sweater it just start the process.

 

Permalink Reply by Gareth on September 22, 2011 at 21:10

There is some interesting data in here

http://forums.roadbikereview.com/wheels-tires/tour-magazine-test-20...

If i get board i my tabulate it so it is easier to read.

Bit disappointed with the Mavic Ksyrium R-Sys SL. Light, stiff, accelerate fast but not good in the aero test. I guess that is what you get for big flat spokes.

Would like to see how the Dura-ace 7900 C24 / C35 / C50 perform using this method. How much better then the Shimano Ultegra WH-6700 which are nearly half the price?

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